The present invention concerns turbocharger systems, such as systems for use with automotive engines. More particularly, the invention concerns a system for diagnosing abnormal compressor performance within the turbocharger.
Turbochargers for diesel and gasoline engines are well known. In a typical automotive turbocharger, radial inflow turbines are driven by engine exhaust gas. The turbine then drives a radial compressor that increases the pressure of intake air provided to the engine. It has been found that under certain operating conditions, the use of a turbocharger improves overall engine efficiency and provides increased power, particularly during vehicle acceleration.
The automotive turbocharger operates in the manner of a centrifugal compressor to provide intake air to the engine at pressures above atmospheric. The performance of the compressor element of a typical automotive turbocharger is usually represented by a pressure ratio versus volume flow graph, with compressor efficiency values superimposed. A performance map of a typical centrifugal compressor is depicted in FIG. 2. The overall shape of the map, as defined by the constant speed and constant efficiency lines, is the product of years of empirical development to tailor the characteristics of the compressor to particular engine air requirements. The boundary of the compressor map is determined by the air requirements of the engine within a particular speed range, typically between the idle speed and the full rated load speed.
The left and right boundaries of the compressor map define a surge line and a choke line, respectively. Both of these lines define a limit of stable operation for the turbocharger or compressor. Referring to FIG. 2, reducing air flow to the compressor within the "surge region" to the left of the surge line, produces intermittent pulsation and interruption of steady air flow through the compressor. Increasing the inlet air flow to the right of the compressor map, namely within the "choke region", causes the overall efficiency of the compressor to fall to very low values. In either case, namely with air flow falling within either the surge or choke regions, the output or performance of the compressor is not properly matched to the specific engine.
Turbocharger operation within either the surge or choke regions can result from various failures in the engine control and operation system, such as a leak in the air intake system. In addition, passage into these regions can occur during normal operation of the turbocharger and engine, but when subject to extreme environmental conditions. For instance, a turbocharger exhibits a well known "altitude-compensating" ability in which the turbocharger automatically speeds up and supplies an additional volume of less dense air to the engine as the vehicle is operated at increasing altitudes. However, the typical automotive turbocharger has a limit to its altitude-compensating characteristic. In a typical case, operation at altitudes above 12,000 feet can lead to compressor surge, which can interrupt the air supply to the engine, thereby causing loss of power, excessive exhaust smoke and high exhaust temperature.
Compressor surge or choke conditions can be overcome by modifying the engine operation. For example, a surge condition can be corrected by derating the engine fuel, or by increasing the engine speed to thereby increase the mass air flow through the turbocharger. At the other end of the spectrum, a compressor choke condition can be alleviated by derating engine speed. While altering the engine operation can overcome a surge or choke condition, it does so at a cost to engine performance and fuel economy. It is therefore important to accurately detect the existence of a compressor abnormal condition to avoid unnecessary modification of the engine operation.
The identification of a compressor abnormal operating condition is achieved using data from sensors throughout the power plant system. If the data is suspect, an abnormality may be misdiagnosed, or simply missed. It is therefore important to verify the information used to determine the existence of a compressor surge/choke condition. It is equally important to have a compressor diagnosis system and method that provides an accurate measure of the compressor performance. The need exists in the arena of turbocharger systems, particularly for automotive use, for such a diagnosis system and method.